Ceramic coating compositions and articles coated therewith



all

1 6 8 cross REFERENC EXAMINER.

United States Patent 0 2,995,453 CERAMIC COATING COMPOSITIONS AND ARTICLES COATED THEREWITH Richard D. Noble, Chicago, Samuel W. Bradstreet, Oak Park, and Harold L. Rechter, Chicago, Ill., assignors to Armour Research Foundation of Illinois Institute of Technology, Chicago, 111., a corporation of Illinois No Drawing. Filed June 4, 1957, Ser. No. 663,333

Claims. (Cl. 106-39) .II n. I,

fractory materials such as s e lgt e d oxidns and.silicates in combinatigp yg'th the bindgr ulgsganees. These compositiofis'aie initially deposited as a slurry and after very moderate heating, or in fact without heat being applied in some instances, form refractory coatings, which are either crystalline or non-crystalline, or mixtures of both,

,depending upon the particular mixture which is used. gwe have found that extremely adherent ceramic coatings rmay be produced from the instant compositions most simply by removal of their water content and thus the rather severe heat requirements of the ceramic coating processes of the prior art is not necessary.

To our knowledge, the prior art illustrates that in order to invest a substrate with a ceramic coating a great deal of heating is required. In some instances the ceramic material is fused onto the substrate surface in the form of a glassy, amorphous material whereas in other processes, either the base is heated, or the ceramic particles are directed through a flame onto the surface sought to be coated. Ceramic compositions are sometimes fused or at least brought to their sintering temperature in order to elfect adherence. Such known procedures, with their rather rigorous heat requirements, are expensive and oftentimes require specialized equipment to be useful.

We have found that various selected compositions of silicates and/or refractory oxides may be combined with mixtures of silmxide and a phosphate source to'pr'oduce slurries which readily yield crystalline or non-crystalline ceramic coatings. We find that merely by removing the water content of these compositions by mild heating or where time permits, by sublimation, extremely adherent coatings which possess excellent refractory properties are produced.

In view of the foregoing, one object of the instant invention is to provide novel ceramic coating compositions consisting essentially of a mixture of silica sol and a ource of phosphate such mixture acting asmr s material, and refraciory materials selected from the group composed of silicates and refracto oxides.

Another object of the instant invention is to provide ceramic coating compositions consisting essentially of a mixture of boric oxide and a source oiphosphate, such mixture actiifg'is the binder material, and ret'iactory materials selected from the group composed of silicates and refractory oxides.

Anciliefobie'ro'f the instant invention is to provide various substrate materials coated with crystalline ceramic coatings, wherein such coatings are bonded essentially through both silica molecules and oxygen atoms.

A further object of the instant invention is to provide ceramic coating compositions which are readily formed into coatings by the removal of water therefrom.

Other objects, features, and advantages of the instant invention will become apparent to those skilled in this Patented Aug. 8, 1961 particular art from the following detailed disclosure thereof.

Examples of compositions produced in accordance with the instant invention are as follows:

5 Example I Zircon, -325 mesh gms- 100 Mono-aluminum phosphate, 50% aqueous solution or 20 Colloidal silica, 35% aqueous solution cc 20 Example II Alumina, -325 mesh ..gms 50 Zircon, -325 mesh gms.... 50 Phosphoric acid, 85% H PO cc Colloidal silica, 35% aqueous solution ..cc 20 Example [11 Zirconia, -325 mesh gms 100 0 Mono-aluminum phosphate, 50% aqueous solution cc 20 Colloidal silica, 35% aqueous solution cc 20 Example IV Stabilized zirconia, -325 mesh ....gms 9L Boric oyd' e. gms 10 lvono-alpminum phosphate, 50% aqueous solution no Water c 20 30 Example V V Stabilized zirconia, 325 mesh gms-- 90 Boric oxide gms l0 Colloidal silica, aqueous solution cc 20 35 The compositions of the instant invention are formed into a slurry mixture and then applied to the surface sought to be coated. fiich application may be, for ex ample, by dipping, spraying, or painting, or in fact by any other known means of depositing one material upon another. As above mentioned, once the material has? been applied in order to form those desirable new coatings it is only necessary to remove a portion or all of the water therefrom. Coatings which are extremely coherent inter se and adherent to the substrate material are thus produced.

It should of course be understood that our invention is not limited to the above specific examples of materials, or of their relative concentrations. Practically any reasonable concentration of colloidal silica assists in the operative formation of these coatings and sources of inor- Zircon, -325 mesh grams 100 Mono-aluminum phosphate, 50% aqueous solu- 0 tion m 20 Colloidal silica, 35% aqueous solution cc 20 said mixture yielding a crystalline material upon the removal of water therefromand in interacting upon water 5 removal to form a cohesive coating.

2. A coating composition consisting essentially of a mixture of:

Alumina, -325 mesh ..grams.. 50 Zircon, 325 mesh do 50 Phosphoric acid, H PO -cc 20 Colloidal silica, 35 aqueous solution --cc 20 said mixture yielding a crystalline material upon the removal of water therefrom and interacting upon water removal to form a cohesive coating.

3. A coating composition consisting essentially of a mixture of:

Ziroonia, -325 mesh grams 100 Mono-aluminum phosphate, 50% aqueous solution cc 20 Colloidal silica, 35% aqueous solution -cc 20 said mixture yielding a crystalline material upon the removal of water therefrom and interacting upon water removal to form a cohesive coating.

4. A coating composition consisting essentially of a mixture of:

Stabilized zirconia, 325 mesh grams 90 Boric oxide dn 10 Mono-aluminum phosphate, 50% aqueous solution cc 30 Water 20 said mixture yielding a crystalline material upon the removal of water therefrom and interacting upon Water removal to form a cohesion coating.

5. A coating composition consisting essentially of a mixture of:

Stabilized zirconia, 325 mesh grams-.. 90 Boric a id do-.." 10 Colloidal silica, 35% aqueous solution cc 20 said mixture yielding a crystalline material upon the removal of water therefrom and interacting upon water removal to form a cohesive coating.

References Cited in the file of this patent UNITED STATES PATENTS 

2. A COATING COMPOSITION CONSISTING ESSENTIALLY OF A MIXTURE OF: 